1. Field of the Invention
This invention relates to a safety device for sewing machines such as an overlock sewing machine and the like, and more particularly to a safety mechanism which is adapted to prevent the sewing machine from being inadvertently driven when loopers mounted in the sewing machine are exposed.
2. Description of the Prior Art
An overlock sewing machine with a conventional safety device as shown in FIG. 5 includes a needle N for feeding a sewing thread to a work piece, and upper and lower loopers 1 and 2 for supplying upper and lower threads to form stitches in cooperation with each other. An overlock sewing machine of this class is arranged not only to form overedge stitches S1 by overedging the workpiece as shown in FIG. 6 but also to make double chain stitches S2 as illustrated in FIG. 7.
Formation of the overedge stitches S1 requires setting a chip guard cover 3 (FIG. 5) to a looper cover 5 of the sewing machine. Formation of the double chain stitches S2 requires setting an auxiliary bed 4 (FIG. 8) to a looper cover 5 of the sewing machine.
The looper cover 5 is so mounted on the overlock sewing machine enabling it to be opened and closed. In the overlock sewing machine, as shown in FIG. 5, the looper cover 5 is brought into a closed condition by pulling it toward the operator after the looper cover 5 has been horizontally moved (rightward in FIG. 5). The looper cover 5 serves not only to facilitate setting the threads to the upper and lower loopers 1 and 2 but also to properly protect the upper and lower loopers therewith, which repeatedly moves reciprocally at a high speed on the order of 1,500 rpm during the sewing operation.
In order to ensure safety of the operator, a safety device 10 (FIG. 9) is provided in the overlock sewing machine which is arranged so that the sewing could not actuate unless the looper cover 5 and the chip guard cover 3 (FIG. 5) or the auxiliary bed 14 are properly fitted to the sewing machine. In other words, the sewing machine may be actuated only when the looper cover and chip guard cover or auxiliary bed are properly set.
As is apparent from FIG. 9, the safety device 10 mounted in the overlock sewing machine consists of a safety switch S', an operative lever 11, and a transmission wire 12 in a tube. The safety switch S' is turned to the ON or OFF position to energize or deenergize a drive motor (not shown) provided for driving the sewing machine. The switch controls the sewing machine to render it actuated or not actuated. The operative lever 11 on the looper cover 5 comprises a rod 11a which moves reciprocally, and a spring 11b anchored between opposite ends of the rod 11a to forwardly urge the rod 11a. The transmission wire 12 is received in a tube or sleeve disposed on a cloth plate cover 14 and includes one end opposed to the safety switch S' and the other end facing the operative lever 11.
According to the safety device 10 (FIG. 9) arranged as aforementioned, the rod 11a of the operative lever 11 abuts against one end of the transmission wire 12 so that the other end of the transmission wire 12 is allowed to bring the safety switch S' into the ON position only when the looper cover 5 and the cloth plate cover 14 are properly set. This renders the sewing machine actuated.
A disadvantage of a conventional safety device is complicated fabrication which is unable to accommodate the transmission wire 12 and the like therein thus entailing a higher production cost due to expensive pans.
A further disadvantage is that the sewing machine must afford more space to accommodate therein the longitudinally extending transmission wire 12 thereby involving difficulty in mounting the chip guard cover 3 and the auxiliary bed 4 and decreasing efficiency of the sewing machine.
A still further disadvantage is that the sewing machine is susceptible to inadvertent movement thus entailing danger to the operator when the looper cover is not well fitted to the frame of the sewing machine.